Electronic signal shaping circuit



Sept. 27, 19 9- c. H. SMITH, JR., ETAL 2,482,303

ELECTRONIC SIGNAL SHAPING CIRCUIT Filed Sept. 13, 1946 is u o l5 25 1|SIGNAL SOURCE fi W l- |2 l8 I3 A SIGNAL FROM SOURCE n 5+ I B AVE. PLATEI SYMMETRICAL VOLTAGE V SQUARE WAVE OUTPUT MIN.PLAIE 1 VOLTAGE I B+--AVE.PLATE UNSYMMETR|CAL C VOLTAGE SQUARE WAVE OUTPUT MIN. PLAT E VOLTAGEgrvue/wbow CARL HARRISON SMITH JR. MILTON L KUDER Patented Sept. 27 1949ELECTRONIC SIGNAL SHAPING CIRCUIT Carl Harrison Smith, Jr., Va, andMilton L. Kuder, Washingttm, D.

Application September 13, 1 94's, Serial No. 696,980

(01. ear-2r) (Granted under the act of March .3, 1883, .as amended April30, 1928 337 0,. G. 757

3 Claims.

invention relates to electrical signal generating systems and inparticular to systems for producing symmetrical square-Wave signals over.a wide frequency range and independent of variations in power linevoltage.

many of the present forms of electrical square-wave signal generatorsystems, a sinus- .oidal signal having thefrequency of the desiredsquare wave signal is first generated andthen applied to -a-cl=ippingstage or stages wherethe crests of the sinusoidal signal areclipp.ed01f. For biasing considerations in the clipper stages it has usuallybeen necessarywith previous systems to maintain the amplitude of thesinusoidal signal applied thereto substantially constant otherwise anon-symmetrical square =wave output is .obtained. To maintain such adegree of constancy in prior systems despite fluctuations such as insupply voltage, special oscillator control tubes or a regulated powersupply were required.

Accordingly it is an object of the presentinvention to provide a signalgenerating system for producing symmetrical square wave signalsindependently .of fluctuations in the voltages supplied thereto. g

Another object of the present invention is .to provide in a square Wavesignal generator system employing a clipper tube, bias adjusting meansfor the clipper tube maintainingsymmetr-ical square wave signal output.

Other and further objects and features of the present invention willbecomeapparent upon a careful consideration of the accompanyingdescription and drawing.

Fig. in a schematic diagram,.pa rtly in block,.

of a typical embodiment of ithe'features of the invention. "1v

Fig. 2 is'a s-eries of waveforms taken to illustrate more fully theoperation of the circuit of Fig. l and the method of maintaining asubstantially symmetrical square wave voltage output.

In accordancewiththe fundamental concepts of the present invention as'igna'l generator device for producing square wave signals is providedin which a symmetrical square wave output is maintained over a widefrequency range despite variations in voltages supplied thereto.Broadly, a reference frequency signal of a sinusoidal character isprovided-to control the operation of the system. This sinusoidal signalis then applied to a clipper tube Where the positive and negative crestsare removed. Bits for the clipper tube is supplied in part from theplate circuit thereof through albias transfer network. This bias isvaried automatically in dependency on the shape of the output squarewave to maintain a central :cl-ipping-regirm resulting in the productionof symmetrical square wave signals. V

With reference to the particular embodiment oi Fig. 1, a clipping tubeL0 is employed :as an overedriven voltage amplifier obtaining its griddrive voltage from :a signal source H through .a coupling-capacitance.:Signal source l is preferably adapted to produce a sinusoidal signalhaving a frequency equal to that-of'the desired square wave outputsignal. Where it is desired that the frequency of the square wave bevariable over a frequency range, the signal source 'll :be

capable of covering that frequency range. The

amplitude of the sinusoidal signal is preferably constant, however theclipper circuit will operate satisfactorily despite wide variations ofinput signal amplitude :and frequency such as would accompanyfluctuations in the supply voltage.

The anode of tube II] is returned to a source of positive voltagethrough anode load resistance M. Voltage fluctuations at the anode oftube Ml are coupled to the output terminals l 5 through a coupling(capacitance 1B andv the ground return lead. I

Bias for the control grid of tube i0 is obtained in part from thepositive supply through anode load resistance l4 and grid couplingresistance I1 and in part from the capacitance 1'2 which becomes chargedas .a result of grid current flow in tube l1] during .a portion of thesinusoidal input signal.

The sinusoidal signal from source ill as represented by waveform A ofFig. 3 drives clipper tube Ill to alternate conditions of heavy anodecirconductivity and anode circuit cut-off. The positive crests of theinput signal drive the controlltnr id of tube 18 positive with respecttothe cathode resulting in control grid conduction and monster-lent lossof signal voltage across limiting resistance 13- to produce theflattened out nega- Ftiue portions of Waveform B, Fig. 2. 0n theopposits half cycles of the driving signal the -clipper tube all! isdriven to a condition of anode :cir-

cuit cut-ofi to produce the flattened positive portions of waveform .13.

Mom wavetorm Bit is evident that :the circuit as ltliiHS far describedproduce a symmetrical square Wave, having durations of the negative andthe positive flattened portions only when the bias of tube I0 iscritically adjusted so that the average grid potential :is midwaybetween required for anode current cut-on and for zero bias conditionand is brought about by the action resistance! 1 to offset "the chargingof capacitance l2 during the periods of grid current flow. When theaverage bias voltage of tube It] is not equal to this mid-value, anunsymmetrical waveform may be produced such as that of C, Fig. 2 inwhich the lower flattened portions are of shorter duration than theupper flattened portions.

To minimize fluctuations in the average bias voltage for tube 10 as aresult of variations in the amplitude of the signal from source II andattendant alternation in the average grid current drawn by tube I 9, thegrid coupling resistance I1 is returned to the anode of the tube.Resistance I1 is purposely made large so as to operate with capacitancel2 as an integrator circuitto hold to a minimum the amount of the outputsquare wave fed back to the junction point I8 yet permit flow of aunilateral charging current for capacitance 12 to counteract thecharging thereof due to the flow of grid current within tube III. Intypical operation, an increase in the amplitude of the signal fromsource ll would tend to raise the portion of the input signal ofwaveform A utilized for the production of the square waveform andconsequently shorten the conduc tivity period of the tube l0. Suchoperation would result in the production of the unsymmetrical squarewave signal of waveform C hav ing a raised average level. Thisdistortion of the signal is counterbalanced by the action of theconnecting path between point [8 and the anode of tube Ill. Theattempted rise in average potential at the anode of tube It] raises thepotential towards which capacitance l2 charges during the time intervalthat the control grid of tube I is non-conductive and hence tends toadjust the bias to restore the desired condition in which the centralportion of the signal from source ll causes the production of the outputsquare wave.

Satisfactory operation of the apparatus of the invention constructed inaccordance with the schematic diagram of Fig. 1 was realized with anoutput signal from source I 1 variable over the frequency range of 2000to 50,000 cycles per second and over the amplitude range of 20 to 200volts with the following circuit constants:

Electron tube-Type 681-17 Anode voltage supply-250 v. v CapacitanceI2--0.25 microfarad Resistance l3--100,000 ohms Resistance Id-22,000ohms Resistance Il-4=.5 megohms From the foregoing discussion it isapparent that considerable modification of the features of the presentinvention is possible and while the device herein described and the formof apparatus for the operation thereof constitutes a preferredembodiment of the invention it is to be understood that the invention isnot limited to this particular device and form of apparatus and thatchanges may be made therein without departing from the scope of theinvention as defined in the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalities thereon or therefor.

What is claimed is:

1. A generator device for producing symmetrical square wave electricalsignals, comprising; a signal generator device for producing sinusoidalsignals of variable amplitude having frequency 4 correspondence with thefrequency of the desired square wave signals, a clipper circuitcomprising an electron tube having anode, cathode, and control gridelectrodes suitable for overdriven amplifier operation, an anode voltagesupply for said tube, coupling means transferring the sinusoidal signalto the control grid electrode of said electron tube in sufiicientamplitude to consecutively drive said electron tube to anode currentsaturation and anode current cutoff, said coupling means comprising aseries-connected combination of a capacitive element and a resistiveelement whose free end is connected to the grid electrode of saidelectron tube, an output circuit operatively connected to the anodeelectrode of said electron tube and to the anode voltage supplytherefor, and a resistive element operatively connected between saidoutput circuit and the input circuit for feed-back to said input circuitof a voltage proportional to the average voltage existing in said outputcircuit whereby an average voltage of substantially zero volts ismaintained in the input circuit at a point between the series connectedcapacitive element and the resistive element and whereby the square-wavevoltage signals developed in the output circuit is maintainedsubstantially symmetrical despite frequency and amplitude fluctuationsof said applied sinusoidal signals.

2. A generator device for producing symmetrical square wave signalscomprising a sine wave signal generator, a clipper circuit fed by saidsine wave generator comprising, an electron tube having an anode, acathode, and a grid, a source of anode supply potential, a loadimpedance connecting said anode to said supply potential, meansincluding a series resistance coupling the output of said sine Wavegenerator to the grid of said tube, a second resistance connecting theanode of said tube to the grid thereof through said series resistance, acondenser disposed within the grid circuit of said tube in anintegrating relationship with said second resistance, said secondresistance and said condenser cooperating to change the grid bias onsaid tube in response to changes in average anode potential on said tubeand in a sense corresponding to the sense of anode potential changes.

3. A clipper circuit comprising an electron tube having an anode, acathode, and a grid, a source of anode supply potential, a loadimpedance connecting said anode to said supply potential, a pair ofserially connected resistance elements connecting the anode of said tubeto the grid thereof, a condenser, one plate of which is connected to thejunction of said resistance elements, the other plate of said condenserserving as an input terminal to the circuit, one of said resistanceelements and said condenser cooperating to change the grid bias on saidtube in response to changes in average anode potential on said tube andin a sense corresponding to the sense of anode potential changes.

CARL HARRISON SMITH, JR. MILTON L. KUDER.

REFERENCES CITED UNITED STATES PATENTS Name Date Schlesinger Apr. 4,1939 Number

